Unslung (or maybe Linksys originally) setup the network to run in promiscuous mode. According to Tiersten on IRC this is due to /usr/sbin/download. If you are as uncomfortable with the possibility of having a sniffer on your network as I am you can disable promiscuous mode:
Disable promiscuous mode:
Note: I killed the /usr/sbin/download process. If you run download again it will set the network back to promiscuous mode.
Important: If you kill /usr/sbin/download then the Sercomm upgrade utility will not work unless you restart it. If you've permanently disabled /usr/sbin/download and can't reenable it then the only way to upgrade with newer Unslung versions is to telnet into RedBoot.
---NOTE: Promiscuous mode is not a security 'weakness'. It just means that the network adapter will not discard packets destined for a different MAC address. Normally these packets will be rejected at the hardware level because the OS shouldn't really care about them if it's not operating as a router. All this modification does is force the discarding of non-local destined packets down to the hardware to manage instead of letting them get into the OS.